1. Field of the Invention
The present invention relates to a lens apparatus having an image stabilization function.
2. Description of the Related Art
A conventional image stabilizing apparatus as disclosed in, for example, Japanese Patent Application Laid-Open No. 2002-229089, which is installed in a lens apparatus, detects vibration by using a vibration sensor to control a correction lens for decentering an optical axis according to the detected vibration. As the vibration sensor, an angular velocity sensor that mainly outputs an analog signal is used, and when vibration occurs, the angular velocity sensor detects an angular velocity and outputs signal according to the vibration. The output signal of the angular velocity is converted into a vibration angle signal by integration, and the vibration angle signal thus obtained is used for calculating a control amount of the correction lens. This control data is used for controlling a driving device such as a motor, to thereby correct an image blur.
Further, there is proposed such an operation that whether or not the lens apparatus is in a pan/tilt operation is automatically determined based on a vibration signal obtained from the vibration sensor, and when it is determined that the lens apparatus is in the pan/tilt operation, a mode of correction for an image blur is switched to an appropriate one. In an example of the proposed operation, when it is determined that the lens apparatus is in the pan/tilt operation, the correction for the image blur is stopped to prevent the image on the screen from becoming unnatural because of the correction for the image blur performed during the pan/tilt operation, and to improve operability of the pan/tilt operation. Whether or not the lens apparatus is in the pan/tilt operation is determined by, for example, detecting whether or not the intensity of the vibration signal obtained from the vibration sensor continues to exceed a predetermined threshold amount for a fixed period of time or longer.
In the case where the correction for the image blur is stopped as a result of the determination that the lens apparatus is in the pan/tilt operation, when it is then determined that the pan/tilt operation is finished, the correction for the image blur is resumed automatically. This operation is favorable because no manual operation is required to resume the correction for the image blur. In Japanese Patent Application Laid-Open No. 2002-229089, for example, when it is detected that the intensity of the vibration signal obtained from the vibration sensor remains below the predetermined threshold amount for the fixed period of time or longer, it is determined that the pan/tilt operation is finished, which triggers the resumption of the correction for the image blur.
In Japanese Patent Application Laid-Open No. 2003-005243, the pan/tilt operation causes a large increase in output from the vibration sensor, and accordingly the output after integration is saturated. After that, vibration cannot be detected. Therefore, when the output from the vibration sensor becomes equal to or larger than a predetermined amount (pan/tilt start determination), the calculation is reset to reduce the signal, and after the calculation is suspended until the vibration is attenuated (pan/tilt stop determination), the calculation of the vibration signal is performed again.
However, when the vibration sensor detects large vibration caused by the pan/tilt operation or the like, the vibration sensor outputs an undesired signal even when the vibration has stopped, and accordingly the output does not promptly return to a reference amount. The reference amount refers to a reference signal output when no vibration occurs. As described in Japanese Patent Application Laid-Open Nos. 2002-229089 and 2003-005243, as a result of using the vibration sensor to determine the stop of the pan/tilt operation, a delay occurs inevitably between the actual stop of the pan/tilt operation and the stop determined based on the output from the vibration sensor. Thus, there arises a problem that an image blur is not corrected for several seconds after an operator has finished the pan/tilt operation. The pan/tilt operation is performed in order to obtain an intended frame composition, and therefore it is a serious disadvantage that an image blur cannot be corrected at the moment that the intended frame composition is obtained. Further, a change in image attributed to the pan/tilt operation is also corrected until the start of the pan/tilt operation is detected, which leads to a problem that the image does not respond to the pan/tilt operation.